Migrate CUSTOM_SYS_INIT_SP_ADDR to Kconfig using system-constants.h

- Make all users of CUSTOM_SYS_INIT_SP_ADDR reference SYS_INIT_SP_ADDR
- Introduce HAS_CUSTOM_SYS_INIT_SP_ADDR to allow for setting the stack
  pointer directly, otherwise we use the common calculation.
- On some platforms that were using the standard calculation but did not
  set CONFIG_SYS_INIT_RAM_SIZE / CONFIG_SYS_INIT_RAM_ADDR, set them.
- On a small number of platforms that were not subtracting
  GENERATED_GBL_DATA_SIZE do so now via the standard calculation.
- CONFIG_SYS_INIT_SP_OFFSET is now widely unused, so remove it from most
  board config header files.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/at91sam9261ek.h b/include/configs/at91sam9261ek.h
index 2089fe5..563fff5 100644
--- a/include/configs/at91sam9261ek.h
+++ b/include/configs/at91sam9261ek.h
@@ -26,8 +26,8 @@
 /* SDRAM */
 #define CONFIG_SYS_SDRAM_BASE		0x20000000
 #define CONFIG_SYS_SDRAM_SIZE		0x04000000
-#define CONFIG_SYS_INIT_SP_ADDR \
-	(ATMEL_BASE_SRAM + 16 * 1024 - GENERATED_GBL_DATA_SIZE)
+#define CONFIG_SYS_INIT_RAM_SIZE	(16 * 1024)
+#define CONFIG_SYS_INIT_RAM_ADDR	ATMEL_BASE_SRAM
 
 /* NAND flash */
 #ifdef CONFIG_CMD_NAND